Line lockout circuit

Claim 2

A line lockout circuit for connection between a subscriber''s line and the line circuit normally assigned to the line at a telephone exchange to disconnect the line from the line circuit in response to the removal of a ground connection from the sleeve lead of the line circuit by other equipment in the exchange and thereafter to keep the line disconnected so long as it is in an off hook condition, said lockout circuit comprising: a. a relay having an operate winding capable of picking up the relay, and a hold winding capable of holding the relay in its picked up condition, b. a set of contacts on said relay normally connecting the line to the line circuit, and, when the relay is picked up, disconnecting the line from the line circuit and connecting one lead of the line to ground and the other lead of the line to one terminal of said hold winding, the other terminal of said hold winding being connected to a current source at a potEntial different from ground, and c. means responsive to removal of a ground connection from the sleeve lead momentarily to energize said operate winding.

Claim 3

A line lockout circuit according to claim 1 wherein said means includes a transistor having its collector-to-emitter current path connected in series with said operate winding, and a capacitor arranged to render said transistor strongly conductive for a brief interval immediately following removal of a ground connection from the sleeve lead.

Claim 4

A lockout circuit for connection to the tip, ring and sleeve leads of a link between stages of a multistage switching network, wherein telephone circuits are connected to one end of the network for connection through the network to common equipment connected to the other end of the network, said lockout circuit being responsive to the removal of a hold signal from the sleeve lead while a telephone circuit connected through the link is in an off hook condition for disabling the link as long as the off hook condition exists, said lockout circuit comprising: a. a relay having an operate winding and a hold winding; b. a set of contacts on said relay normally interconnecting the tip and ring leads of the link between the stages of said network and, when the relay is picked up, opening the tip and ring leads and connecting one of said tip and ring leads to one power terminal and the other one of the tip and ring leads to one terminal of said hold winding, the other terminal of said hold winding being connected to another power terminal, and c. circuit means responsive to removal of a hold signal from the sleeve lead to momentarily energize said operate winding causing the relay to pick up.

Claim 5

A lockout circuit for connection to the tip, ring and sleeve leads of a link between stages of a multistage switching network, wherein telephone circuits are connected to one end of the network for connection through the network to common equipment connected to the other end of the network, said lockout circuit being responsive to the removal of a hold signal from the sleeve lead while a telephone circuit connected through the link is in an off hook condition for disabling the link as long as the off hook condition exists, said lockout circuit comprising: a. a relay having an operate winding and a hold winding; b. a set of contacts on said relay normally interconnecting the tip and ring leads of the link between the stages of said network and, when the relay is picked up, opening the tip and ring leads and connecting one of said tip and ring leads to one power terminal and the other one of the tip and ring leads to one terminal of said hold winding, the other terminal of said hold winding being connected to another power terminal, and c. circuit means responsive to removal of a hold signal from the sleeve lead to momentarily energize said operate winding causing the relay to pick up.

Claim 6

A lockout circuit according to claim 3 wherein said circuit means includes a transistor having its collector-to-emitter current path connected in series with said operate winding, and a capacitor arranged to render said transistor conductive for a brief interval immediately following removal of a ground connection from the sleeve lead to operate said relay.

Claim 7

A lockout circuit according to claim 4 including circuit means interconnecting the collector of said transistor, said sleeve lead and said ground connection so that a hold signal is applied to said sleeve lead via said transistor in the interim period between the removal of said hold signal from said sleeve lead and the operation of said relay and thereafter the hold signal is applied directly to said sleeve lead until the off hook condition is terminated.

Claim 8

A telephone lockout circuit comprising: a. a relay having operate and hold coils; b. circuit means for connecting of said relay to tip and ring leads so that when the relay is unoperated the circuit through the tip and ring leads is completed and when said relay is operated the tip and ring leads are open circuited and one of the tip and ring leads is connected to a power terminal while the other of the tip and ring leads is connected through the hold winding to another power terminal, and c. circuit means for connecting said operate coil of said relay to a sleeve lead so that when a hold signal is removed from said sleeve lead, the operate coil is momentarily energized to actuate the relay.

Claim 9

A telephone lockout circuit comprising: a. a relay having operate and hold coils; b. circuit means for connecting of said relay to tip and ring leads so that when the relay is unoperated the circuit through the tip and ring leads is completed and when said relay is operated the tip and ring leads are open circuited and one of the tip and ring leads is connected to a power terminal while the other of the tip and ring leads is connected through the hold winding to another power terminal, and c. circuit means for connecting said operate coil of said relay to a sleeve lead so that when a hold signal is removed from said sleeve lead, the operate coil is momentarily energized to actuate the relay.

Claim 10

A telephone lockout circuit according to claim 6 wherein said circuit means for connecting said operate coil of said relay to the sleeve lead includes a transistor having its collector-to-emitter circuit path connected in series with said operate winding, and a capacitor arranged to render said transistor conductive for a brief interval immediately following removal of a hold signal from the sleeve lead to operate said relay.

Claim 11

A lockout circuit for isolating a telephone line from common switching equipment in a telephone exchange whenever a closed loop path through said telephone line exists and no attempt is made to complete a call within a prescribed period comprising: a. circuit means connected in series with the electrical Path between said telephone line and said common switching equipment for interrupting said electrical path; b. latching circuit means coupled to said circuit means and said electrical path such that the actuation of said latching circuit means in response to a momentary signal causes said circuit means to interrupt said electrical path and wherein said latching circuit means remains actuated so long as a closed loop path exists through said telephone line, and c. switching circuit means connected between said latching circuit means and said common switching equipment responsive to removal of a hold signal applied to said switching circuit means by said telephone exchange to apply a momentary signal to actuate said latching circuit means.

Claim 12

A lockout circuit for isolating a telephone line from common switching equipment in a telephone exchange whenever a closed loop path through said telephone line exists and no attempt is made to complete a call within a prescribed period comprising: a. circuit means connected in series with the electrical Path between said telephone line and said common switching equipment for interrupting said electrical path; b. latching circuit means coupled to said circuit means and said electrical path such that the actuation of said latching circuit means in response to a momentary signal causes said circuit means to interrupt said electrical path and wherein said latching circuit means remains actuated so long as a closed loop path exists through said telephone line, and c. switching circuit means connected between said latching circuit means and said common switching equipment responsive to removal of a hold signal applied to said switching circuit means by said telephone exchange to apply a momentary signal to actuate said latching circuit means.

Claim 13

A lockout circuit according to claim 8: a. wherein said latching circuit means includes a dual coil lockout relay having an operate winding and a hold winding, said hold winding being connected in series with said telephone line between the terminals of a DC power source when said operate winding is energized, and b. wherein said switching circuit means includes a transistor whose collector-emitter path is connected in series with the operate winding of said lockout relay between the terminals of the DC power source so that said relay is actuated when said transistor is turned on.

Claim 14

A lockout circuit according to claim 9 wherein said circuit means includes a pair of normally closed contacts of said lockout relay, each one of said contacts being connected in series with one conductor of said electrical path and includes a pair of normally open contacts of said lockout relay, one of said normally open contacts being connected between one of the conductors of said electrical path and a ground terminal of the DC power source and the other of said contacts being connected between the other conductor of said electrical path and one terminal of said hold winding.

Claim 15

A lockout circuit according to claim 9 wherein said switching circuit means includes a resistive-capacitive circuit connected to said common switching equipment and the base of said transistor so that when the hold signal applied thereto is removed, a capacitor is charged from the DC power source with a polarity designed to forward bias said transistor so that said transistor is rendered conductive momentarily.